You need a sim or hotspot your phone to the car. Volvo on call has its own sim which is covered under the subscription - first three years should be free, but I think some finance companies have it removed for price. On call sim only covers on call.

P.S: In-car Spotify is premium account only - you can't use free version.

So there is a seperate Sim for the On Call as there is in the boot?

Yep, the On Call has the SIM in a tamper-proof location somewhere behind the dash I believe. The slot in the boot is completely separate, should you want to use your own data SIM for the apps, map updates, etc.